One of the primary uses of petroleum is as fuel. As the average carbon dioxide levels have already gone above 400 ppm and global warming is taking place, there have been many calls to reduce the usage of petroleum by substituting it with renewable energy. Biofuels stand very distinct among all other renewables because they could be easily used as a drop in replacement for petroleum based fuels.

Petroleum usage

Around 84 percent of the distillates are used as fuels including diesel, gasoline(petrol), kerosene, LPG etc. Considering the oil usage at 94 million barrels per day, this amounts to 4585 billion litres per year.

Biofuel yield

Different biofuel crops have different yields. Typical values are given below.

Land Requirement to replace the entire petroleum based fuel

Considering the above yield and the amount of petroleum used as fuel, total land usage of different crops to replace the entire petroleum based fuel could be calculated. For comparison two forms of other data is also provided. 1) Total arable and agricultural land available. 2) Land area of some of the larger countries in the world.

Could Brazil increase the ethanol production 100 times utilizing the entire area of Brazil itself? Otherwise could the entire Sahara Desert or the United States be used for producing palmoil based biodiesel? Could any of these options be possible without touching the remaining tropical rainforests in the world?

As far as land usage is concerned, algae is the only source with a potential to replace the entire petroleum usage. But it is still a reasearch topic for many years, far away from being commerically available.

Usage of exotic Chemistries and Rare Materials:
Many of the materials used are rare and expensive, for example Platinum is used as a catalyst in Fuel cells, usage of composite materials in flywheels, rare earths in superconductors etc.

Environmental issues:
Batteries use environmentally unfriendly chemicals. Prime examples are the usage of Lead and Cadmium. Extremely reactive metals like Sodium and Lithium also are used.

Safety Issues:
Many of the fuel cells and batteries should be operated at high temperatures. Reactive metals like Sodium and Lithium have safety concerns.

Limited Cycles:
Most of the batteries could only be used for a limited number of cycles, for example Lead Acid Batteries have a limit of around 800 cycles.

Bad Depth of Discharge:
They could not be 100% discharged, Deep Cycle Batteries could go to around 20% charge

Low Energy Density:
Energy Densities are very low compared to both fossil fuels and biofuels.

Does that mean that we could dump the whole idea of energy storage itself? Hold on for a second, let us see what are the alternatives available.

What about maintaining the current status quo?
We are using fossil fules like petroleum, coal and natural gas to meet majority of our energy requirements. They have many advantages which could not be ignored for now, mainly comparatively cheap, excellent energy density, easy to store/carry wherever required etc. Most of the infrastructure required are already there.

To give an overview, currently huge amounts of fossil fuels are getting used. World usage of petroleum is around 86 Million Barrels per Day. To make it simple, 1000 barrels of oil is getting burnt every second !!!!! Coal usage is an astouding 6 Billion Metric Tonnes per year, that is 1 Metric Tonne per person. India alone uses around 3 Million Barrels of oil per day and 250 Million tonnes of coal every year.

So, if are ready to forget about pollution, climate change and expendable nature of fossil fuels, we still would be able to continue drinking petrol, eating coal and breathing natural gas. That is the only way to maintain current status quo.

Hydropower is really clean, should we use it?
Hydropwer is the single largest renewable energy source currently under use. It accounts for 20% of both India’s and World’s electricity production. Hydropower has a total potential to supply around 100% of installed capacity (around 3000GW) of the world. So water could barely lift the current load.Hydro Potential of IndiaHydro Potential of World

Nuclear Power Scenario
Nuclear Power provides around 14% of World’s electricity. Nuclear enjoyed lots of interests until recently. But after the Japanese Fukushima Nuclear Crisis, serious safety concerns have been raised.

How about using biomass like agricultural by-products, manure etc.
Biomass has got a huge potential and we should try to utilize them. A study says that India produces around 500 MMT of biomass per year and out of which around 150 MMT is surplus. This gives a potential of around 25000 MW electricity production for India.Biomass Potential of India
But, looking carefully, biomass is really a low hanging fruit. It looks fantastic until biomass based systems try to go real mainstream. Once they reach the mainstream status, they could potentially create the following problems.

Limited amount of biomass availability because they are mainly agricultural by-products. So further scaling up from the above numbers would be really difficult.

Direct competition with food production for the availability of land if biomass production becomes a profitable business.

Stepping upon forest land for the same reason.

Difficult to use in transportation sector.

Can we complement the situation with Biofuels?
There are many different types of biofules available like bioethanol, biodiesel and biobutanol. Current main source of ethanol are sugar cane, and corn. Where as biodiesel could be produced from different oil sources like sunflower, coconut oil, palm oil etc. and also from Jatropha from marginal lands. But the best yield is given by different algae streams.
One study says that Jatropha based biodisel cound supply 22% of India’s petroleum demand.Jatropha Potential of India

Considering the usage of land, it is essential to look at the overall efficiency from sunlight to biodiesel. It is practically less than 1%Photosynthesis Efficiency

So, only algae based Biofules could reach sustainability. It is progressing but still it has not reached commercial status.
Other biofuel technologies like sugar cane ethanol, corn ethanol, palm oil and other biodiesel etc. have limited potential to fix the overall energy issues. Apart from that, they also contribute to the above mentioned problems: encroaching upon forest and farm land.

Our Earth is too hot inside. Geothermal energy.
Geothermal is another often discussed (pseudo) renewable energy and it could be considered as a baseload resource with no energy storage requirement. For commerical/quality power generation deep wells are required, on the other hand shallow wells could be used for heating purpose.
All these come with a few drawbacks. As per wikipedia, even though geothermal potential is much more than the current energy requirement, only a fraction of that is recoverable. Also quality varies through geographic locations. Apart from the economics, there are potential environmental drawbacks also. Chances of trapped carbon dioxide, sulphur dioxide etc. getting released to the environment is high. In addition to these gases toxic elements like Mercury, Arsenic etc. could get released. There have been concerns about increased earthquakes due to deep wells.Environmental Effects of Geothermal EnergyGeothermal Resources

Wave Power, OTEC and Tidal Power
Wave Power, Tidal Power and Ocean Therman Energy Conversion (OTEC) have great energy potential. But they have not reached commercial status yet. Only pilot projects of a few MWs have been carried out so far.

How about Solar and Wind?
As per Harvard University, Wind Energy has a potential of more than 40 times the current World energy consumption. Where as Earth receives around 6000 times Solar Energy compared to the energy consumption. Wind Power has already reached grid parity in many cases and solar is gearing towards that. Lots of reserach and investments are taking place to make them go mainstream.Global Potential for WindpowerWindpower PotentialSolar Potential

So, Sustainability and Climate Change have defined a clear goal…… Reduce the above oil and coal usage numbers as much and as fast as possible. A very challenging problem, much more than any “Rocket Science” ever achieved.

Considering both the current state of technology development and overall potential to meet the global energy demand completely, only Solar and Wind could be considered for the top positions. But their sustainability depends upon Energy Storage.

So as far as Energy Storage is concerned, apart from biting the bullet no other solution is existing in the long run. There is no other way, but to fix all of the shortcoming of Energy Storage.

Edited on 08/08/2011
I received a comment about Solar Thermal systems. Solar could include both Photovoltaic and concentrated solar thermal systems also.